Governmental regulations typically require that public water supplies be tested and monitored for turbidity. Generally speaking, turbidity is the measure of small particulate matter suspended in a liquid, which matter causes light passing through the liquid to be scattered or absorbed. Conventional nephelometric turbidimeters operate by projecting a light beam through a water sample. A detector is placed at an angle to the light beam such that it measures the scattering or reflecting of light caused by the particulate matter in the liquid.
A number of problems are encountered by known turbidimeters, particularly those that are used in the field, such as at water filtration plants. For example, most turbidimeters employ an encased light source which periodically fails. Changing the light source can be an aggravating and time consuming procedure, which requires opening the housing of the turbidimeter to access the light source. This can subject the electronics of the apparatus to moisture and contamination. Additionally, when the light source is changed the turbidimeter must be recalibrated. This is very often a messy procedure which involves the handling and mixing of carcinogenic substances such as Formanzin.
A further problem experienced by conventional turbidimeters is their tendency to exhibit erroneous readings, particularly in humid environments. Typically, the water sample is introduced into the turbidimeter in a glass cuvette. When a cuvette containing relatively cold water is exposed for cleaning, calibration etc., the humid outside air tends to cause condensation to form on the cuvette. This often results in erroneously high measurements.
Monitoring filter backwash also presents difficulties in the field. Filter backwash refers to the percentage of light transmitted through water backwashed through the filter. A filtration system must be backwashed at frequent intervals to clean the filter when it becomes clogged. Measuring turbidity and backwash are mutually exclusive tasks since turbidity has no meaning during backwash. Accordingly, in most cases, the backwash monitor includes its own electronics, which are entirely separate from the turbidimeter. As a result, the water filtration system requires a complex array of sensors and analyzing electronics. Presently, no compact and conveniently usable monitoring system is known for selectively measuring turbidity and backwash.
The indicator displays used by most turbidimeters are likewise problematic, particularly for providing an accurate history of the turbidity of the water supply. Known apparatuses often employ a strip chart recorder that records the turbidity measured at predetermined time intervals. However, it is possible that the recorded turbidity may be a spurious high or low reading and may not accurately reflect the average turbidity during the time period in question. As a result, the recorded history may not be entirely accurate.